Nitrate production and accumulation in lettuce as affected by mineral Nitrogen supply and organic fertilization

Abstract

Lettuce is one of the leading vegetables in Brazil. However, studies concerning its fertilization for the Northeastern region of the country are still scarce. This work was carried out to evaluate the effects of mineral Nitrogen supply and organic fertilization on the production and nitrate accumulation in lettuce, cultivar Elba, in the semi-arid zone of Paraíba, Brazil. A randomized block design, with four replications, was used to test five doses of cattle manure (30; 60; 90; 120, and 150 t ha -1 ), five doses of N supplied as urea (30; 60; 90; 120, and 150 kg ha -1 ), and a control without fertilization. Along with mineral N, the other nutrients were also supplied using mineral sources. No additional nutrients were supplied where organic fertilization was used. Lettuce yield was significantly higher when organic fertilization was used, compared to the mineral nutrient supply. Taking into account most of the fertilization doses recommended for growing lettuce in the Brazilian Northeastern States, N mineral fertilization in sandy soils with low organic matter contents can be fully replaced by organic fertilization with cattle manure. Plant total (PTY) and commercial yield (PCY) as affected by the mineral N supply fitted into a quadratic model, in which the doses 94.5 and 95.7 kg ha -1 corresponded to respectively the highest PTY (381.9 g plant -1 ) and PCY (321.6 g plant -1 ). Where organic fertilization was used, PTY and PCY fitted into a linear model. Therefore, the highest PTY (523.9 g plant -1 ) and PCY (449.48 g plant -1 ) were observed at the highest manure doses. Nitrate content on roots, stems, and leaves increased linearly with Nitrogen and manure application. In roots, the nitrate content (mg kg -1 of fresh matter) reached 93.96 (N mineral (Nm)) and 65.09 (organic fertilization (OF)); in stems, 183.45 (Nm) and 98.22 (OF); and in leaves, 121.98 (Nm) and 75.62 (OF). The maximum nitrate content observed in leaves was far below the risk level for human health.

Response of Cape gooseberry (Physalis peruviana L.) to nitrogen application under sandy soil conditions

“…The differences in N-uptake between the treatments were stronger than the differences in N-content in dry weight due to the yield differences. This is in agreement with results of Porto et al (2008). The authors investigated the effects of five doses of N (30, 60, 90, 120 and 150 kg ha -1 ) on lettuce plants grown under sandy soil and found that nitrate content in roots, stems and leaves increased linearly with nitrogen application.…”

“…Nitrogen application under sandy soil conditions was studied extensively for other vegetable crops including onion (Mahmoud 2006;Khalil et al 2007;Khalil 2008;Brar et al 2008), lettuce (Porto et al 2008), pepper and tomato (Zhang et al 2006;Zotarelli et al 2007), bean (Podsiado et al 2007), zucchini (Zotarelli et al 2007), and potato (Alva 2006;Badawy and Ahmed 2006). However, while for tomatoes and other crops there generally exists a lot of information and practical recommendations, the literature sources for husky tomatoes are very limited.…”

Produtividade e acúmulo de nitrato nos frutos de abobrinha em função da adubação nitrogenada

“…Incremento no teor de nitrato em função de doses de N tem sido preconizado na literatura para diferentes hortaliças, como repolho, espinafre (Chen et al, 2004), alface (Pôrto et al, 2008), tomate (Ferreira et al, 2006), dentre outras.…”

Cinza vegetal na germinação e no desenvolvimento da alface

“…Conforme apresentado na análise química, este produto é rico em P e possui uma boa proporção de matéria orgânica. Além disso, Porto et al (2008) comentaram que plantas de alface cultivadas com esterco bovino como fonte de N foram mais produtivas do aquelas cultivadas com uma fonte mineral destes nutrientes. 1,94 7,53 ns -não significativo; *significativo pelo testes F a 5% de probabilidade pelo teste ; ** significativo pelo teste F a 1% de probabilidade; Médias seguidas de mesma letra, na coluna, não diferem estatisticamente entre si pelo teste Tukey a 5% de probabilidade.…”